This invention relates generally to pumps which act on flexible bags to dispense fluent material, and more particularly to a liquid dispenser employing a flexible bag suitable for higher flow rate operation.
Pumps are often used in applications where the surfaces contacting a fluent material being pumped should be kept clean. Such fluent materials include food, beverages, and medicinal products in the form of liquids, powders, slurries, dispersions, particulate solids or other pressure transportable fluidizable material. For instance, where the fluent material is a food additive for a food product, it is imperative that surfaces contacting the material are maintained in an aseptic condition. Accordingly, the parts of the pump which contact the food are made of materials (e.g., stainless steel) which are highly resistant to corrosion and can be cleaned.
It is known to isolate the material from the pump by having the pump act on a flexible bag containing the fluent material, rather than on the fluent material itself. There are many examples in the context of delivery of medicines. Co-pending and co-assigned U.S. patent application Ser. No. 09/909,422, filed Jul. 17, 2001, Ser. No. 09/978,649, filed Oct. 16, 2001, Ser. No. 10/156,732, filed May 28, 2002 and Ser. No. 10/351,006, filed Jan. 24, 2003 disclose pumps of this general type and illustrate applications in the handling of food and products other than medicine. The disclosure of these applications is incorporated herein by reference. Use of pumps of this general type is also desirable, even when it is not necessary to maintain aseptic conditions.
The application of pumps of the aforementioned type outside the field of medicine often requires higher flow rates. The flow rates may produce fluid flow effects which act on the flexible bag in ways which are detrimental to its operation. For instance, the bag material may tend to collapse under pressure drops caused by rapid fluid flow rates. It is desirable to be able to perform several manipulations of the fluent material in the flexible bag, such as mixing of two component materials. Handling of the fluent material in this manner requires valving which operates without direct contact with the fluent material. If the fluent material is liquid containing particulate matter, the particulate matter can block a valve from reaching a fully closed position, causing leakage past the valve. One such example of fluent material containing particulate matter is orange juice which contains pulp. Different juices have differently sized pulp, which presents different problems for sealing. It is desirable to provide flow paths which can be selectively sealed to block flow, but which are not tortuous or otherwise affect the flow in the open, free-flowing condition. Still further, pumps of this general type use vacuum and pressure pumps for applying a vacuum and a positive pressure to the flexible bag to induce flow of fluent material. In many contexts, it is less desirable to employ vacuum pumps and pressure pumps because they require space and can generate undesirable noise.
In one application, the flexible bag may contain a concentrate which is diluted by water (or another diluent) added to the concentrate. If another fluid is to be supplied to the flexible bag in use, a connection is necessary. Fittings to make such connections require additional structure and additional time to make the connection. Moreover, it is imperative that the connections not leak either upon connection or disconnection. Different concentrates often require different dilution ratios. Conventionally, changes in dilution ratios are achieved by dedicating a pump to a particular type of concentrate or by physically altering the pump.